High-performance detection of ultraviolet (UV) radiation is of great
importance for a wide range of applications including flame sensing,
environmental (ozone layer) monitoring, detection of biological/chemical agents,
missile early warning systems, and secure intersatellite communication systems.
These applications require high-performance UV photodetectors with low dark
current, high responsivity, high detectivity, and fast time response. The widebandgap
AlxGa1−xN ternary alloy is well-suited as a photodetector material for
operation in the wavelength range of 200 nm to 365 nm. Its outstanding material
properties (direct bandgap, tunable cut-off, allows heterostructures, intrinsically solar-blind) make AlxGa1−xN suitable for a variety of harsh environments. If
properly constructed, AlxGa1−xN-based photodetectors could offer significant
advantages over the older photomultiplier tube (PMT) technology in terms of size,
cost, robustness, complexity, dark current, bandwidth, and solar-blind operation.
The motivation behind this work is the need for high-performance, solid-state
UV photodetectors that can be cost-effectively manufactured into high-density
arrays. We have designed, fabricated, and characterized several visible/solar-blind
AlxGa1−xN photodiode samples. With solar-blind AlxGa1−xN photodiode samples,
we achieved excellent device performance in almost all aspects. Very low dark
currents were measured with heterostructure AlxGa1−xN Schottky and p-i-n
samples. The extremely low leakage characteristics resulted in record detectivity
and noise performance. Detectivity performance comparable to PMT detectivity
was achieved. True solar-blind operation (sub-280 nm cut-off) with high visible
rejection was demonstrated. In addition, we improved the bandwidth performance
of AlxGa1−xN-based solar-blind photodetectors by over an order of magnitude.
Solar-blind Schottky, p-i-n, and metal-semiconductor-metal photodiode samples
exhibited very fast pulse response with multi-GHz bandwidths.